The stethoscope is one of the most recognizable tools in the physician's art. The heart, lungs, arteries, and joints emit sounds useful in diagnostic procedures. In order to be able to quickly focus on the particular sounds and to help the physician discriminate between normal and pathological sounds, the stethoscope art developed versatile instruments. For example, there are many stethoscopes which can either emphasize or de-emphasize particular frequency ranges depending on the physician's need of the moment.
One of the best known techniques for accomplishing this desirable versatility is to incorporate more than one sound collecting component or microphone into the chestpiece of the stethoscope. The two most conventional types of microphones are the diaphragm type, which has a thin, round disc of material defining a sound collecting surface, and the bell type, which as an open, concave shape. The lip of the bell defines a sound collecting surface that helps funnel acoustic energy toward passageways that carry sound to the ears. The bell type microphone conveys the lowest tones, such as the main "lub-dup" of the heartbeat. The diaphragm type microphones are most typically tuned to de-emphasize those lowest tones and to pass tones of slightly higher frequency. This helps the user of the stethoscope to more readily perceive the sounds typical of heart valve pathologies.
It is well known in the art to place a bell and diaphragm microphone on the chestpiece so as to increase the versatility of the stethoscope. It is also well known to employ microphones with sound collecting surfaces of different sizes. A large microphone is usually better at collecting the most acoustical energy, but a small microphone may be helpful if the patient is very small, or if the part of the body being contacted is bony, or if the site producing the sound must be localized very specifically, or if the site is located in a remote position that is difficult for the healthcare worker to reach.
When more than one microphone is present, the microphones should be conveniently arranged and the user should be able to rapidly choose between the microphones. U.S. Pat. No. 4,770,270 to Grimm discloses one bell type and one diaphragm type microphone placed on diametrically opposite sides of a chestpiece. A user switches between them by rotating a stem that connects the chestpiece to a binaural. It is also known to provide one bell type and one diaphragm type microphone on generally, but not diametrically, opposite sides of the chestpiece, and to arrange for selection between them. U.S. Pat. No. 2,505,124 to Lepeschkin; U.S. Pat. No. 3,630,308 to Ravin; and U.S. Pat. No. 4,212,368 to Allen disclose prior art arrangements. Two microphones can be in the same plane as shown in U.S. Pat. No. Des. 208,125 to Cefaly, or in perpendicular planes as shown in U.S. Pat. No. 2,513,827 to Tynan.
A limitation of all of these devices is the inconvenience involved in switching the orientation of the chestpiece in space to apply one microphone after another, and the inconvenience involved in switching between the active and inactive microphone. Coassigned U.S. Pat. No. 4,440,258 discloses a diaphragm mounted on a flexible surround within the microphone. The stethoscope can readily switch between one response and the other by slight adjustments in the pressure applied by the user's hand against the chestpiece in contact with the patient's body.